The properties of heavy oils and bitumen have long been known, in general, they have a low API gravity, high asphaltene content, low middle distillate yield, high sulphur content, high nitrogen content and high metal content. A typical Athabasca bitumen may contain 51.5 wt % material boiling above 524 C, 4.48 wt % sulphur, 0.43 wt % nitrogen, 213 ppm vanadium and 67 ppm nickel. These heavy oils are very viscous, they require enhanced oil recovery techniques such as steam injection and, as a result stable oil/water emulsions are formed. The first process in oil production is the breakup of these emulsions to meet pipeline specs. Generally the water is removed by a combination of gravity separation and addition of demulsifiers to break the emulsion, these are often difficult and costly chemical and mechanical treatments. After, a water free oil has been obtained, the viscosity and density pipeline specifications are met by the addition of a diluent. The heavy oil is now ready for transport to be processed. Among the prior art broad categories of heavy oil upgrading processes already known are: carbon rejection, hydrogen addition and gasification. Carbon rejection processes include: delayed coking, fluid coking, and other versions of heavy oil cracking. Hydrogen addition processes include: hydrocracking and hydrotreating. Gasification processes include; direct and indirect combustion.
In the carbon rejection process, heavy oil is converted to distillates and coke, they typically remove more than 20% of the feed material as coke, this represents an excessive waste of resources. In hydrogen addition processes, and in the presence of catalysts an external source of hydrogen (typically generated from natural gas) is added to increase the hydrogen to carbon ratio, reduce sulphur and nitrogen content, and prevent the formation of coke. Examples of hydrogen addition processes include: fixed bed catalytic hydroconversion; ebullated catalytic bed hydroconversion and thermal slurry hydroconversion. These processes differ from each from: operating conditions, liquid yields, catalysts compositions, reactor designs, heat transfer, mass transfer, etc., the objective being to decrease the molecular weight of large fractions to produce lighter fractions and remove sulphur and nitrogen. In gasification processes, the objective is to convert the heavy fractions into lighter fractions using a heat carrier, there are two methods; direct and indirect. Examples of direct and indirect gasification processes for heavy oil operations are; the heavy to light HTL process an indirect process which has two vessels; a gasifier and a combustor, sand is re-circulated between the gasifier and the combustor as the heat transferring medium and the OrCrude Upgrading a direct process where the heavy fractions are converted into syngas on a contact gasifier.
Of all the above processes the most common in the industry are the carbon rejection and hydrogen addition processes. In carbon rejection, delayed coking is the preferred process. The hydrogen addition processes are continuously improving from ebbulated to slurry with the development of new catalysts. The gasification processes are relatively new in the heavy oil industry and not yet established as a process of choice. The delayed coking process is an established process that produces unstable distillate products, they require stabilization via hydrotreating, moreover it has lower liquid yields due to the high generation of coke, typically over 20% of the feed material. The hydrogen addition processes, typically require a steam reformer plant to generate high pressure hydrogen for the reaction with hydrocarbons in the presence of selective catalysts. These processes typically operate at high pressures and temperatures, generating liquid yields in excess of 100%. The major operation challenge in the hydrogen addition processes is the deactivation of the catalysts due to the impurities present in the feed such as; sulfur, nitrogen and metals. As the catalyst becomes deactivated it must be removed and regenerated, catalyst regeneration is usually done offsite by catalysts manufacturers.